Investments (details) - OTTI Rollforward (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	$ 160	$ 143	$ 152	$ 135
Additions for OTTI securities where no credit losses were previously recognized				2
Additions for OTTI securities where credit losses have been previously recognized	1	5	7	10
Reductions due to sales/defaults of credit-impaired securities	(1)		(1)	(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	2	2	4	4
Cumulative OTTI credit losses recognized for securities still held, end of period	162	150	162	150
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	61	51	58	47
Additions for OTTI securities where credit losses have been previously recognized		4	3	8
Reductions due to sales/defaults of credit-impaired securities	(1)		(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	1		1
Cumulative OTTI credit losses recognized for securities still held, end of period	61	55	61	55
All other corporate bonds [Member]
Roll-forward of the credit component of other-than-temporary impairments on fixed maturities recognized in the consolidated statement of income for which a portion of the other-than-temporary impairment was recognized in other comprehensive income [Roll Forward]
Cumulative OTTI credit losses recognized for securities held, beginning of period	99	92	94	88
Additions for OTTI securities where no credit losses were previously recognized				2
Additions for OTTI securities where credit losses have been previously recognized	1	1	4	2
Reductions due to sales/defaults of credit-impaired securities				(1)
Adjustments to book value of credit-impaired securities due to changes in cash flows	1	2	3	4
Cumulative OTTI credit losses recognized for securities still held, end of period	$ 101	$ 95	$ 101	$ 95